by Dr. Manura Nanayakkara

Created on: October 25, 2010

This is the popular brand name of the over the counter generic drug Diphenhydramine. This medication is a first generation antihistamine. It is used in symptomatic relief of allergies such as colds, sneezing, coughs, hay fever, watery eyes and allergic rhinitis. In addition, benadryl is a common ingredient in over the counter cough medications.

This medication is available as tablets as well as syrup form for children. Severity of the side effects are more with children and elderly.

How Benadryl works?

This drug acts by blocking naturally occurring chemical called histamine in the body.  In addition, it crosses to the brain, so sedation and drowsiness are common side effects.

What are the things you need to consider before taking Benadryl?

If you have Kidney diseases, Liver diseases, enlarged prostate gland, glaucoma, or epilepsy then you should not take this medication without a doctor’s advice. In addition, you should not take this if you are pregnant or nursing unless prescribed by a doctor.

What are the common side effects?

Drowsiness is the commonest side effect of Benadryl. So do not operate machinery or drive while on Benadryl, until you know how it affects you. In addition do not take alcoholic beverages or any other CNS depressant drugs such as Valium or Ambien.

In addition Benadryl can cause urinary retention. So do not take this medication if you have enlarged prostate gland.

Headache, urinary retention, and blurred vision are also common side effects. Naso pharyngitis, fatigue and dry mouth are common side effects as well. Gastro intestinal disturbances like nausea can occur with some patients.

Take this medication only in recommended dosage without exceeding the dose. Do not eat high fat meal at the time of taking the drug. High fat meals decreases blood concentration of above medication.

What are the side effects that are not so common?

Rarely somnolence, fatigue, and reduced energy are reported. Sometimes patients can get low blood pressure, increased heart rate, cardiac rhythm abnormalities, and abnormal movements. Dizziness, confusion, and depression can occur in few patients. Sleep disturbance is another troublesome side effect that can occur rarely. Very rarely patients can get tremors and convulsions (fits).

Rare side effects that are specific to Benadryl are exforliative dermatitis (skin peeling off), tinnitus, short term blood pressure reduction, and abnormal Central nervous system stimulation.

Pregnancy and breast feeding

Although there are no evidence of fetal harm, manufacturer advice to avoid during pregnancy.  Especially in the first three months. Significant amount is present in breast milk and manufacturer advices to avoid.

Summary

Benadryl is a common antihistamine in many over the counter cough preparations. But it has some nasty side effects such as severe drowsiness, so it is advisable not to take it without doctor’s prescription. In addition it is also advisable to look into the ingredients section of any cough syrup to see, whether it contain Diphenhydramine or Benadryl.

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